Micro-electromechanical valve having transformable valve actuator

ABSTRACT

A micro-electromechanical valve is provided having a channel defined by a substrate and circuitry thereon so as to terminate at an aperture, a closure member arranged to be displaceable between first and second positions at which the aperture is respectively covered and uncovered and fluid is respectively inhibited and permitted from flowing through the channel, and an elongate actuator for displacing the closure member between the first and second positions. One end of the actuator is anchored to the substrate and the other end is connected to the closure member. A portion of the actuator in electrical contact with the circuitry is configured to transform between straightened and arcuate shapes when respectively heated and cooled by respective receipt and withdrawal of electrical current from the circuitry. The actuator displaces the closure member between the first and second positions in response to the transformation of the portion.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a Continuation Application of U.S. application Ser. No.10/884,887 filed Jul. 6, 2004, which is a Continuation Application ofU.S. application Ser. No. 10/693,947, filed on October 28, 2003, nowissued U.S. Pat. No. 6,783,217,which is a Continuation Application ofU.S. application Ser. No. 10/302,606, filed on Nov. 23, 2002, now issuedU.S. Pat. No. 6,644,767, which is a Continuation Application of U.S.application Ser. No. 09/855,094, filed on May 14, 2001, now issued U.S.Pat. No. 6,485,123, which is a Continuation-in-Part of U.S. applicationSer. No. 09/112,815, now issued U.S. Pat. No. 6,247,792, filed on Jul.10, 1998.

CROSS REFERENCES TO RELATED APPLICATIONS

The following Australian provisional patent applications are herebyincorporated by reference. For the purposes of location andidentification, US patents/patent applications identified by their USpatent/patent application serial numbers are listed alongside theAustralian applications from which the US patents/patent applicationsclaim the right of priority. CROSS-REFERENCED US PATENT/PATENTAUSTRALIAN APPLICATION (CLAIMING PROVISIONAL RIGHT OF PRIORITY PATENTFROM AUSTRALIAN DOCKET APPLICATION NO. PROVISIONAL APPLICATION) NO.PO7991 09/113,060 ART01 PO8505 6,476,863 ART02 PO7988 09/113,073 ART03PO9395 6,322,181 ART04 PO8017 09/112,747 ART06 PO8014 6,227,648 ART07PO8025 09/112,750 ART08 PO8032 09/112,746 ART09 PO7999 09/112,743 ART10PO7998 09/112,742 ART11 PO8031 09/112,741 ART12 PO8030 6,196,541 ART13PO7997 6,195,150 ART15 PO7979 6,362,868 ART16 PO8015 09/112,738 ART17PO7978 09/113,067 ART18 PO7982 6,431,669 ART19 PO7989 6,362,869 ART20PO8019 6,472,052 ART21 PO7980 6,356,715 ART22 PO8018 09/112,777 ART24PO7938 09/113,224 ART25 PO8016 6,366,693 ART26 PO8024 6,329,990 ART27PO7940 09/113,072 ART28 PO7939 6,459,495 ART29 PO8501 6,137,500 ART30PO8500 09/112,796 ART31 PO7987 09/113,071 ART32 PO8022 6,398,328 ART33PO8497 09/113,090 ART34 PO8020 6,431,704 ART38 PO8023 09/113,222 ART39PO8504 09/112,786 ART42 PO8000 6,415,054 ART43 PO7977 09/112,782 ART44PO7934 09/113,056 ART45 PO7990 09/113,059 ART46 PO8499 6,486,886 ART47PO8502 6,381,361 ART48 PO7981 6,317,192 ART50 PO7986 09/113,057 ART51PO7983 09/113,054 ART52 PO8026 09/112,752 ART53 PO8027 09/112,759 ART54PO8028 09/112,757 ART56 PO9394 6,357,135 ART57 PO9396 09/113,107 ART58PO9397 6,271,931 ART59 PO9398 6,353,772 ART60 PO9399 6,106,147 ART61PO9400 09/112,790 ART62 PO9401 6,304,291 ART63 PO9402 09/112,788 ART64PO9403 6,305,770 ART65 PO9405 6,289,262 ART66 PP0959 6,315,200 ART68PP1397 6,217,165 ART69 PP2370 09/112,781 DOT01 PP2371 09/113,052 DOT02PO8003 6,350,023 Fluid01 PO8005 6,318,849 Fluid02 PO9404 09/113,101Fluid03 PO8066 6,227,652 IJ01 PO8072 6,213,588 IJ02 PO8040 6,213,589IJ03 PO8071 6,231,163 IJ04 PO8047 6,247,795 IJ05 PO8035 6,394,581 IJ06PO8044 6,244,691 IJ07 PO8063 6,257,704 IJ08 PO8057 6,416,168 IJ09 PO80566,220,694 IJ10 PO8069 6,257,705 IJ11 PO8049 6,247,794 IJ12 PO80366,234,610 IJ13 PO8048 6,247,793 IJ14 PO8070 6,264,306 IJ15 PO80676,241,342 IJ16 PO8001 6,247,792 IJ17 PO8038 6,264,307 IJ18 PO80336,254,220 IJ19 PO8002 6,234,611 IJ20 PO8068 6,302,528 IJ21 PO80626,283,582 IJ22 PO8034 6,239,821 IJ23 PO8039 6,338,547 IJ24 PO80416,247,796 IJ25 PO8004 09/113,122 IJ26 PO8037 6,390,603 IJ27 PO80436,362,843 IJ28 PO8042 6,293,653 IJ29 PO8064 6,312,107 IJ30 PO93896,227,653 IJ31 PO9391 6,234,609 IJ32 PP0888 6,238,040 IJ33 PP08916,188,415 IJ34 PP0890 6,227,654 IJ35 PP0873 6,209,989 IJ36 PP09936,247,791 IJ37 PP0890 6,336,710 IJ38 PP1398 6,217,153 IJ39 PP25926,416,167 IJ40 PP2593 6,243,113 IJ41 PP3991 6,283,581 IJ42 PP39876,247,790 IJ43 PP3985 6,260,953 IJ44 PP3983 6,267,469 IJ45 PO79356,224,780 IJM01 PO7936 6,235,212 IJM02 PO7937 6,280,643 IJM03 PO80616,284,147 IJM04 PO8054 6,214,244 IJM05 PO8065 6,071,750 IJM06 PO80556,267,905 IJM07 PO8053 6,251,298 IJM08 PO8078 6,258,285 IJM09 PO79336,225,138 IJM10 PO7950 6,241,904 IJM11 PO7949 6,299,786 IJM12 PO806009/113,124 IJM13 PO8059 6,231,773 IJM14 PO8073 6,190,931 IJM15 PO80766,248,249 IJM16 PO8075 09/113,120 IJM17 PO8079 6,241,906 IJM18 PO805009/113,116 IJM19 PO8052 6,241,905 IJM20 PO7948 09/113,117 IJM21 PO79516,231,772 IJM22 PO8074 6,274,056 IJM23 PO7941 6,290,861 IJM24 PO80776,248,248 IJM25 PO8058 6,306,671 IJM26 PO8051 6,331,258 IJM27 PO80456,110,754 IJM28 PO7952 6,294,101 IJM29 PO8046 6,416,679 IJM30 PO93906,264,849 IJM31 PO9392 6,254,793 IJM32 PP0889 6,235,211 IJM35 PP08876,491,833 IJM36 PP0882 6,264,850 IJM37 PP0874 6,258,284 IJM38 PP13966,312,615 IJM39 PP3989 6,228,668 IJM40 PP2591 6,180,427 IJM41 PP39906,171,875 IJM42 PP3986 6,267,904 IJM43 PP3984 6,245,247 IJM44 PP39826,315,914 IJM45 PP0895 6,231,148 IR01 PP0870 09/113,106 IR02 PP08696,293,658 IR04 PP0887 09/113,104 IR05 PP0885 6,238,033 IR06 PP08846,312,070 IR10 PP0886 6,238,111 IR12 PP0871 09/113,086 IR13 PP087609/113,094 IR14 PP0877 6,378,970 IR16 PP0878 6,196,739 IR17 PP087909/112,774 IR18 PP0883 6,270,182 IR19 PP0880 6,152,619 IR20 PP088109/113,092 IR21 PO8006 6,087,638 MEMS02 PO8007 6,340,222 MEMS03 PO800809/113,062 MEMS04 PO8010 6,041,600 MEMS05 PO8011 6,299,300 MEMS06 PO79476,067,797 MEMS07 PO7944 6,286,935 MEMS09 PO7946 6,044,646 MEMS10 PO939309/113,065 MEMS11 PP0875 09/113,078 MEMS12 PP0894 6,382,769 MEMS13

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to a micro-electromechanical valveassembly.

BACKGROUND OF THE INVENTION

Many different types of printing have been invented, a large number ofwhich are presently in use. The known forms of print have a variety ofmethods for marking the print media with a relevant marking media.Commonly used forms of printing include offset printing, laser printingand copying devices, dot matrix type impact printers, thermal paperprinters, film recorders, thermal wax printers, dye sublimation printersand ink jet printers both of the drop on demand and continuous flowtype. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

In recent years, the field of ink jet printing, wherein each individualpixel of ink is derived from one or more ink nozzles has becomeincreasingly popular primarily due to its inexpensive and versatilenature.

Many different techniques on ink jet printing have been invented. For asurvey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

Ink Jet printers themselves come in many different types. Theutilisation of a continuous stream ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electrostatic ink jetprinting.

U.S. Pat. No. 3,596,275 by Sweet also discloses a process of acontinuous ink jet printing including the step wherein the ink jetstream is modulated by a high frequency electro-static field so as tocause drop separation. This technique is still used by severalmanufacturers including Elmjet and Scitex (see also U.S. Pat. No.3,373,437 by Sweet et al)

Piezoelectric ink jet printers are also one form of commonly used inkjet printing device. Piezoelectric systems are disclosed by Kyser et.al. in U.S. Pat. No. 3,946,398 (1970) which discloses a diaphragm modeof operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) whichdiscloses a squeeze mode of operation of a piezoelectric crystal, Stemmein U.S. Pat. No. 3,747,120 (1972) which discloses a bend mode ofpiezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 whichdiscloses a piezoelectric push mode actuation of the ink jet stream andFischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode typeof piezoelectric transducer element.

Recently, thermal ink jet printing has become an extremely popular formof ink jet printing. The ink jet printing techniques include thosedisclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S.Pat. No. 4,490,728. Both the aforementioned references disclose ink jetprinting techniques rely upon the activation of an electrothermalactuator which results in the creation of a bubble in a constrictedspace, such as a nozzle, which thereby causes the ejection of ink froman aperture connected to the confined space onto a relevant print media.Printing devices using the electro-thermal actuator are manufactured bymanufacturers such as Canon and Hewlett Packard.

As can be seen from the foregoing, many different types of printingtechnologies are available. Ideally, a printing technology should have anumber of desirable attributes. These include inexpensive constructionand operation, high speed operation, safe and continuous long termoperation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction operation, durability and consumables.

The valve assembly that forms the basis of this invention facilitatesthe achievement of a number of the desirable attributes listed above.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided anelongate actuator for moving a closure member in amicro-electromechanical valve assembly for controlling a flow of fluidthrough a fluid supply channel, the channel being defined by a wafersubstrate and drive circuitry layers positioned on the wafer substrateand terminating at a fluid supply opening, the actuator having a firstend anchored to the wafer substrate so as to be in electrical contactwith al least one of the drive circuitry layers and a second endconnected to the closure member so as to move it between a closedposition, in which the closure member covers the fluid supply openingand ink is inhibited from flowing through the fluid supply channel, andan open position, in which the fluid supply opening is opened to allowthe ink to flow through the fluid supply channel, wherein

at least a portion of the actuator, in a rest condition, has an arcuateshape and is configured to be heated, upon receiving an electricalcurrent from the drive circuitry, such that when the portion is heatedit expands and causes the actuator to straighten sufficiently todisplace the closure member from closed to an open position; and asubsequent cooling of the portion, after the current is discontinued,causes the actuator to return to its rest condition returning theclosure to the closed position.

According to another aspect of the invention, there is provided amicro-electromechanical valve assembly for controlling a flow of fluidthrough a fluid supply channel defined in a wafer substrate and drivecircuitry layers positioned on the wafer substrate and terminating at afluid supply opening, the valve assembly comprising;

an elongate actuator that is anchored at one end to the wafer substrateto be in electrical contact with the drive circuitry layers; and

a closure member that is mounted on an opposite end of the elongateactuator, the actuator being configured to receive an electrical signalfrom the drive circuitry layer to displace the closure member between aclosed position in which the closure member covers the fluid supplyopening and ink is inhibited from flowing through the fluid supplychannel and an open position, wherein

the elongate actuator is shaped so that, in a rest condition, theactuator encloses an arc, the actuator including a heating portion thatis capable of being heated on receipt of the electrical signal toexpand, the heating portion being configured so that, when the portionis heated, the resultant expansion of the portion causes the actuator tostraighten at least partially and a subsequent cooling of the portioncauses the actuator to return to its rest condition thereby displacingthe closure between the closed and open positions.

Each actuator may include a body portion that is of a resilientlyflexible material having a coefficient of thermal expansion which issuch that the material can expand to perform work when heated, theheating portion being positioned in the body portion and defining aheating circuit of a suitable metal.

The heating circuit may include a heater and a return trace, the heaterbeing positioned proximate an inside edge of the body portion and thereturn trace being positioned outwardly of the heater, so that an insideregion of the body portion is heated to a relatively greater extent withthe result that the inside region expands to a greater extent than aremainder of the body portion.

A serpentine length of said suitable material may define the heater.

The body portion may be of polytetrafluoroethylene and the heatingcircuit may be of copper

Each actuator may define a coil that partially uncoils when the heatingportion expands.

In accordance with a third aspect of the present invention, there isprovided an inkjet nozzle comprising an ink ejection port for theejection of ink, an ink supply with an oscillating ink pressureinterconnected to the ink ejection port, a shutter mechanisminterconnected between the ink supply and the ink ejection port, whichblocks the ink ejection port, and an actuator mechanism for moving theshutter mechanism on demand away from the ink ejection port so as toallow for the ejection of ink on demand from the ink ejection port.

In another embodiment of the invention, there is provided a method ofoperating an ink jet printhead that includes a plurality of nozzlearrangements and an ink reservoir, each nozzle arrangement having:

a nozzle chamber and an ink ejection port in fluid communication withthe nozzle chamber, and

a closure that is operatively positioned with respect to the inkejection port, the closure being displaceable between open and closedpositions to open and close the ink ejection port, respectively,

the ink reservoir in fluid communication with the nozzle chambers, themethod comprising the steps of:

maintaining each closure in the closed position;

subjecting ink in the ink reservoir and thus each nozzle chamber to anoscillating pressure,

selectively and independently displacing each closure into the openposition so that an ink droplet is ejected from the respective inkejection port as a result of the oscillating pressure.

Further, the actuator preferably comprises a thermal actuator which isactivated by the heating of one side of the actuator. Preferably theactuator has a coiled form and is uncoiled upon heating. The actuatorincludes a serpentine heater element encased in a material having a highcoefficient of thermal expansion. The serpentine heater concertinas uponheating. Advantageously, the actuator includes a thick return trace forthe serpentine heater element. The material in which the serpentineheater element is encased comprises polytetrafluoroethylene. Theactuator is formed within a nozzle chamber which is formed on a siliconwafer and ink is supplied to the ejection port through channels etchedthrough the silicon wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of thepresent invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

FIG. 1 is an exploded perspective view illustrating the construction ofa single ink jet nozzle in accordance with the preferred embodiment;

FIG. 2 is a perspective view, partly in section, of a single ink jetnozzle constructed in accordance with the preferred embodiment;

FIG. 3 provides a legend of the materials indicated in FIGS. 4 to 16;

FIG. 4 to FIG. 16 illustrate sectional views of the manufacturing stepsin one form of construction of an ink jet printhead nozzle; and

FIG. 17 shows a schematic, sectional end view of part of an ink jetnozzle array showing two nozzle arrangements of the array;

FIG. 18 shows the array with ink being ejected from one of the nozzlearrangements;

FIG. 19 shows a schematic side view of re-filling of the nozzle of thefirst nozzle arrangement; and

FIG. 20 shows operation of the array preceding commencement of inkejection from the second of the illustrated nozzle arrangements.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment, an oscillating ink reservoir pressure isused to eject ink from ejection nozzles. Each nozzle has an associatedshutter which normally blocks the nozzle. The shutter is moved away fromthe nozzle by an actuator whenever an ink drop is to be fired.

Turning initially to FIG. 1, there is illustrated in explodedperspective a single ink jet nozzle 10 as constructed in accordance withthe principles of the present invention. The exploded perspectiveillustrates a single ink jet nozzle 10. Ideally, the nozzles are formedas an array on a silicon wafer 12. The silicon wafer 12 is processed soas to have two level metal CMOS circuitry which includes metal layersand glass layers 13 and which are planarised after construction. TheCMOS metal layer has a reduced aperture 14 for the access of ink fromthe back of silicon wafer 12 via an ink supply channel 15.

A bottom nitride layer 16 is constructed on top of the CMOS layer 13 soas to cover, protect and passivate the CMOS layer 13 from subsequentetching processes. Subsequently, there is provided a copper heater layer18 which is sandwiched between two polytetrafluoroethylene (PTFE) layers19,20. The copper layer 18 is connected to lower CMOS layer 13 throughvias 25,26. The copper layer 18 and PTFE layers 19,20 are encapsulatedwithin nitride borders e.g. 28 and nitride top layer 29 which includesan ink ejection port 30 in addition to a number of sacrificial etchedaccess holes 32 which are of a smaller dimension than the ejection port30 and are provided for allowing access of a etchant to lowersacrificial layers thereby allowing the use of the etchant in theconstruction of layers, 18,19,20 and 28.

Turning now to FIG. 2, there is shown a cutaway perspective view of afully constructed ink jet nozzle 10. The ink jet nozzle uses anoscillating ink pressure to eject ink from ejection port 30. Each nozzlehas an associated shutter 31 which normally blocks it. The shutter 31 ismoved away from the ejection port 30 by an actuator 35 whenever an inkdrop is to be fired.

The ports 30 are in communication with ink chambers which contain theactuators 35. These chambers are connected to ink supply channels 15which are etched through the silicon wafer. The ink supply channels 15are substantially wider than the ports 30, to reduce the fluidicresistance to the ink pressure wave. The ink channels 15 are connectedto an ink reservoir. An ultrasonic transducer (for example, apiezoelectric transducer) is positioned in the reservoir. The transduceroscillates the ink pressure at approximately 100 KHz. The ink pressureoscillation is sufficient that ink drops would be ejected from thenozzle were it not blocked by the shutter 31.

The shutters are moved by a thermoelastic actuator 35. The actuators areformed as a coiled serpentine copper heater 23 embedded inpolytetrafluoroethylene (PTFE) 19/20. PTFE has a very high coefficientof thermal expansion (approximately 770×10⁻⁶). The current return trace22 from the heater 23 is also embedded in the PTFE actuator 35, thecurrent return trace 22 is made wider than the heater 23 and is notserpentine. Therefore, it does not heat the PTFE as much as theserpentine heater 23 does. The serpentine heater 23 is positioned alongthe inside edge of the PTFE coil, and the return trace is positioned onthe outside edge. When actuated, the inside edge becomes hotter than theoutside edge, and expands more. This results in the actuator 35uncoiling.

The heater layer 23 is etched in a serpentine manner both to increaseits resistance, and to reduce its effective tensile strength along thelength of the actuator. This is so that the low thermal expansion of thecopper does not prevent the actuator from expanding according to thehigh thermal expansion characteristics of the PTFE.

By varying the power applied to the actuator 35, the shutter 31 can bepositioned between the fully on and fully off positions. This may beused to vary the volume of the ejected drop. Drop volume control may beused either to implement a degree of continuous tone operation, toregulate the drop volume, or both.

When data signals distributed on the printhead indicate that aparticular nozzle is turned on, the actuator 35 is energized, whichmoves the shutter 31 so that it is not blocking the ink chamber. Thepeak of the ink pressure variation causes the ink to be squirted out ofthe nozzle 30. As the ink pressure goes negative, ink is drawn back intothe nozzle, causing drop break-off. The shutter 31 is kept open untilthe nozzle is refilled on the next positive pressure cycle. It is thenshut to prevent the ink from being withdrawn from the nozzle on the nextnegative pressure cycle.

Each drop ejection takes two ink pressure cycles. Preferably half of thenozzles 10 should eject drops in one phase, and the other half of thenozzles should eject drops in the other phase. This minimises thepressure variations which occur due to a large number of nozzles beingactuated.

Referring to FIGS. 17 to 20, the operation of the printhead is describedin greater detail. The printhead comprises an array of nozzlearrangements or nozzles 10, two of which are shown as 10.1 and 10.2 inFIG. 17. Each nozzle arrangement 10 has a chamber 58 in which itsassociated shutter 31 is arranged.

Each chamber 58 is in communication with an ink reservoir 60 via an inksupply channel 36. An ultrasonic transducer in the form of apiezoelectric transducer 62 is arranged n the ink reservoir 60.

As described above, each ink drop ejection takes two ink pressurecycles. The two ink pressure cycles are referred to as a phase. Half ofthe nozzles 10 should eject ink drops 64 (FIG. 18) in one phase with theother half of the nozzles ejecting ink drops in the other phase.

Consequently, as shown in FIG. 17 of the drawings, the shutter 31.2 ofthe nozzle 10.2 is in an open position while the shutter 31.1 of thenozzle 10.1 is in its closed position. It will be appreciated that thenozzle 10.2 represents all the open nozzles of the array of theprinthead while the nozzle 10.1 represents all the closed nozzles of thearray of the printhead.

In a first pressure cycle, the transducer 62 is displaced in thedirection of arrows 66 imparting positive pressure to the ink 57 in thereservoir 60 and, via the channels 36, the chambers 58 of the nozzles10. Due to the fact that the shutter 31.2 of the nozzle 10.2 is open,ink in the ink ejection port 30.2 bulges outwardly as shown by themeniscus 68. After a predetermined interval, the transducer 62 reversesdirection to move in the direction of arrows 70 as shown in FIG. 18 ofthe drawings. This causes necking, as shown at 72, resulting inseparation of the ink drop 64 due to a first negative going pressurecycle imparted to the ink 57.

In the second positive pressure cycle, as shown in FIG. 19 of thedrawings, with the transducer moving again in the direction of arrow 66,the positive pressure applied to the ink results in a refilling of thechamber 58.2 of the nozzle 10.2. It is to be noted that the shutter 31.2is still in an open position with the shutter 31.1 still being in aclosed position. In this cycle, no ink is ejected from either nozzle10.1 or 10.2.

Before the second negative pressure cycle, as shown in FIG. 20 of thedrawings, the shutter 31.2 moves to its closed position. Then, as thetransducer 62 again moves in the direction of arrows 70 to impartnegative pressure to the ink 57, a slight concave meniscus 74 is formedat both ink ejection ports 30.1 and 30.2 However, due to the fact thatboth shutters 31.1 and 31.2 are closed, withdrawal of ink from thechambers 58.1 and 58.2 of the nozzles 10.1 and 10.2, respectively, isinhibited.

The amplitude of the ultrasonic transducer can be altered in response tothe viscosity of the ink (which is typically affected by temperature),and the number of drops which are to be ejected in the current cycle.This amplitude adjustment can be used to maintain consistent drop sizein varying environmental conditions.

The drop firing rate can be around 50 KHz. The ink jet head is suitablefor fabrication as a monolithic page wide printhead. FIG. 2 shows asingle nozzle of a 1600 dpi printhead in “up shooter” configuration.

Returning again to FIG. 1, one method of construction of the ink jetprint nozzles 10 will now be described. Starting with the bottom waferlayer 12, the wafer is processed so as to add CMOS layers 13 with anaperture 14 being inserted. The nitride layer 16 is laid down on top ofthe CMOS layers so as to protect them from subsequent etchings.

A thin sacrificial glass layer is then laid down on top of nitridelayers 16 followed by a first PTFE layer 19, the copper layer 18 and asecond PTFE layer 20. Then a sacrificial glass layer is formed on top ofthe PTFE layer and etched to a depth of a few microns to form thenitride border regions 28. Next the top layer 29 is laid down over thesacrificial layer using the mask for forming the various holes includingthe processing step of forming the rim 40 on nozzle 30. The sacrificialglass is then dissolved away and the channel 15 formed through the waferby means of utilisation of high density low pressure plasma etching suchas that available from Surface Technology Systems.

One form of detailed manufacturing process which can be used tofabricate monolithic ink jet printheads operating in accordance with theprinciples taught by the present embodiment can proceed using thefollowing steps:

1. Using a double sided polished wafer 12, complete drive transistors,data distribution, and timing circuits using a 0.5 micron, one poly, 2metal CMOS process 13. The wafer is passivated with 0.1 microns ofsilicon nitride 16. This step is shown in FIG. 4. For clarity, thesediagrams may not be to scale, and may not represent a cross sectionthough any single plane of the nozzle. FIG. 3 is a key torepresentations of various materials in these manufacturing diagrams,and those of other cross referenced inkjet configurations.

2. Etch nitride and oxide down to silicon using Mask 1. This maskdefines the nozzle inlet below the shutter. This step is shown in FIG.5.

3. Deposit 3 microns of sacrificial material 50 (e.g. aluminum orphotosensitive polyimide)

4. Planarize the sacrificial layer to a thickness of 1 micron overnitride. This step is shown in FIG. 6.

5. Etch the sacrificial layer using Mask 2. This mask defines theactuator anchor point 51. This step is shown in FIG. 7.

6. Deposit 1 micron of PTFE 52.

7. Etch the PTFE, nitride, and oxide down to second level metal usingMask 3. This mask defines the heater vias 25, 26. This step is shown inFIG. 8.

8. Deposit the heater 53, which is a 1 micron layer of a conductor witha low Young's modulus, for example aluminum or gold.

9. Pattern the conductor using Mask 4. This step is shown in FIG. 9.

10. Deposit 1 micron of PTFE 54.

11. Etch the PTFE down to the sacrificial layer using Mask 5. This maskdefines the actuator and shutter This step is shown in FIG. 10.

12. Wafer probe. All electrical connections are complete at this point,bond pads are accessible, and the chips are not yet separated.

13. Deposit 3 microns of sacrificial material 55. Planarize using CMP

14. Etch the sacrificial material using Mask 6. This mask defines thenozzle chamber wall 28. This step is shown in FIG. 11.

15. Deposit 3 microns of PECVD glass 56.

16. Etch to a depth of (approx.) 1 micron using Mask 7. This maskdefines the nozzle rim 40. This step is shown in FIG. 12.

17. Etch down to the sacrificial layer using Mask 6. This mask definesthe roof of the nozzle chamber, the nozzle 30, and the sacrificial etchaccess holes 32. This step is shown in FIG. 13.

18. Back-etch completely through the silicon wafer (with, for example,an ASE Advanced Silicon Etcher from Surface Technology Systems) usingMask 7. This mask defines the ink inlets 15 which are etched through thewafer. The wafer is also diced by this etch. This step is shown in FIG.14.

19. Etch the sacrificial material. The nozzle chambers are cleared, theactuators freed, and the chips are separated by this etch. This step isshown in FIG. 15.

20. Mount the printheads in their packaging, which may be a moldedplastic former incorporating ink channels which supply the appropriatecolor ink to the ink inlets at the back of the wafer. The package alsoincludes a piezoelectric actuator attached to the rear of the inkchannels. The piezoelectric actuator provides the oscillating inkpressure required for the ink jet operation.

21. Connect the printheads to their interconnect systems. For a lowprofile connection with minimum disruption of airflow, TAB may be used.Wire bonding may also be used if the printer is to be operated withsufficient clearance to the paper.

22. Hydrophobize the front surface of the printheads.

23. Fill the completed printheads with ink 57 and test them. A fillednozzle is shown in FIG. 16.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the preferred embodiment without departing from the spirit orscope of the invention as broadly described. The present embodiment is,therefore, to be considered in all respects to be illustrative and notrestrictive.

The presently disclosed ink jet printing technology is potentiallysuited to a wide range of printing systems including: colour andmonochrome office printers, short run digital printers, high speeddigital printers, offset press supplemental printers, low cost scanningprinters, high speed pagewidth printers, notebook computers with inbuiltpagewidth printers, portable colour and monochrome printers, colour andmonochrome copiers, colour and monochrome facsimile machines, combinedprinter, facsimile and copying machines, label printers, large formatplotters, photograph copiers, printers for digital photographic‘minilabs’, video printers, PhotoCD printers, portable printers forPDAs, wallpaper printers, indoor sign printers, billboard printers,fabric printers, camera printers and fault tolerant commercial printerarrays.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Ofcourse many different devices could be used. However presently popularink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal inkjet is power consumption.This is approximately 100 times that required for high speed, and stemsfrom the energy-inefficient means of drop ejection. This involves therapid boiling of water to produce a vapor bubble which expels the ink.Water has a very high heat capacity, and must be superheated in thermalinkjet applications. This leads to an efficiency of around 0.02%, fromelectricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size andcost. Piezoelectric crystals have a very small deflection at reasonabledrive voltages, and therefore require a large area for each nozzle.Also, each piezoelectric actuator must be connected to its drive circuiton a separate substrate. This is not a significant problem at thecurrent limit of around 300 nozzles per printhead, but is a majorimpediment to the fabrication of pagewidth printheads with 19,200nozzles.

Ideally, the ink jet technologies used meet the stringent requirementsof in-camera digital color printing and other high quality, high speed,low cost printing applications. To meet the requirements of digitalphotography, new ink jet technologies have been created. The targetfeatures include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systemsdescribed below with differing levels of difficulty. Forty-fivedifferent inkjet technologies have been developed by the Assignee togive a wide range of choices for high volume manufacture. Thesetechnologies form part of separate applications assigned to the presentAssignee as set out in the table under the heading Cross References toRelated Applications.

The ink jet designs shown here are suitable for a wide range of digitalprinting systems, from battery powered one-time use digital cameras,through to desktop and network printers, and through to commercialprinting systems.

For ease of manufacture using standard process equipment, the printheadis designed to be a monolithic 0.5 micron CMOS chip with MEMS postprocessing. For color photographic applications, the printhead is 100 mmlong, with a width which depends upon the ink jet type. The smallestprinthead designed is IJ38, which is 0.35 mm wide, giving a chip area of35 square mm. The printheads each contain 19,200 nozzles plus data andcontrol circuitry.

Ink is supplied to the back of the printhead by injection molded plasticink channels. The molding requires 50 micron features, which can becreated using a lithographically micromachined insert in a standardinjection molding tool. Ink flows through holes etched through the waferto the nozzle chambers fabricated on the front surface of the wafer. Theprinthead is connected to the camera circuitry by tape automatedbonding.

Tables of Drop-On-Demand Ink Jets

Eleven important characteristics of the fundamental operation ofindividual ink jet nozzles have been identified. These characteristicsare largely orthogonal, and so can be elucidated as an elevendimensional matrix. Most of the eleven axes of this matrix includeentries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of inkjet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains36.9 billion possible configurations of ink jet nozzle. While not all ofthe possible combinations result in a viable ink jet technology, manymillion configurations are viable. It is clearly impractical toelucidate all of the possible configurations. Instead, certain ink jettypes have been investigated in detail. These are designated IJ01 toIJ45 above which matches the docket numbers in the table under theheading Cross References to Related Applications.

Other ink jet configurations can readily be derived from theseforty-five examples by substituting alternative configurations along oneor more of the 11 axes. Most of the IJ01 to IJ45 examples can be madeinto ink jet printheads with characteristics superior to any currentlyavailable ink jet technology.

Where there are prior art examples known to the inventor, one or more ofthese examples are listed in the examples column of the tables below.The IJ01 to IJ45 series are also listed in the examples column. In somecases, a print technology may be listed more than once in a table, whereit shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Homeprinters, Office network printers, Short run digital printers,Commercial print systems, Fabric printers, Pocket printers, Internet WWWprinters, Video printers, Medical imaging, Wide format printers,Notebook PC printers, Fax machines, Industrial printing systems,Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrixare set out in the following tables. ACTUATOR MECHANISM (APPLIED ONLY TOSELECTED INK DROPS) Description Advantages Disadvantages ExamplesThermal An electrothermal Large force High power Canon Bubblejet bubbleheater heats the ink to generated Ink carrier 1979 Endo et al GB aboveboiling point, Simple limited to water patent 2,007,162 transferringsignificant construction Low efficiency Xerox heater-in- heat to theaqueous No moving parts High pit 1990 Hawkins et ink. A bubble Fastoperation temperatures al U.S. Pat. No. 4,899,181 nucleates and quicklySmall chip area required Hewlett-Packard forms, expelling the requiredfor actuator High mechanical TIJ 1982 Vaught et ink. stress al U.S. Pat.No. 4,490,728 The efficiency of the Unusual process is low, withmaterials required typically less than Large drive 0.05% of theelectrical transistors energy being Cavitation causes transformed intoactuator failure kinetic energy of the Kogation reduces drop. bubbleformation Large print heads are difficult to fabricate Piezoelectric Apiezoelectric crystal Low power Very large area Kyser et al U.S. Pat.No. such as lead consumption required for actuator 3,946,398 lanthanumzirconate Many ink types Difficult to Zoltan U.S. Pat. No. (PZT) iselectrically can be used integrate with 3,683,212 activated, and eitherFast operation electronics 1973 Stemme expands, shears, or Highefficiency High voltage U.S. Pat. No. 3,747,120 bends to apply drivetransistors Epson Stylus pressure to the ink, required Tektronixejecting drops. Full pagewidth IJ04 print heads impractical due toactuator size Requires electrical poling in high field strengths duringmanufacture Electrostrictive An electric field is Low power Low maximumSeiko Epson, used to activate consumption strain (approx. Usui et all JPelectrostriction in Many ink types 0.01%) 253401/96 relaxor materialssuch can be used Large area IJ04 as lead lanthanum Low thermal requiredfor actuator zirconate titanate expansion due to low strain (PLZT) orlead Electric field Response speed magnesium niobate strength requiredis marginal (˜10 μs) (PMN). (approx. 3.5 V/μm) High voltage can begenerated drive transistors without difficulty required Does not requireFull pagewidth electrical poling print heads impractical due to actuatorsize Ferroelectric An electric field is Low power Difficult to IJ04 usedto induce a phase consumption integrate with transition between the Manyink types electronics antiferroelectric (AFE) can be used Unusual andferroelectric (FE) Fast operation materials such as phase. Perovskite(<1 μs) PLZSnT are materials such as tin Relatively high requiredmodified lead longitudinal strain Actuators require lanthanum zirconateHigh efficiency a large area titanate (PLZSnT) Electric field exhibitlarge strains of strength of around 3 V/μm up to 1% associated can bereadily with the AFE to FE provided phase transition. ElectrostaticConductive plates are Low power Difficult to IJ02, IJ04 plates separatedby a consumption operate electrostatic compressible or fluid Many inktypes devices in an dielectric (usually air). can be used aqueous Uponapplication of a Fast operation environment voltage, the plates Theelectrostatic attract each other and actuator will displace ink, causingnormally need to be drop ejection. The separated from the conductiveplates may ink be in a comb or Very large area honeycomb structure,required to achieve or stacked to increase high forces the surface areaand High voltage therefore the force. drive transistors may be requiredFull pagewidth print heads are not competitive due to actuator sizeElectrostatic A strong electric field Low current High voltage 1989Saito et al, pull is applied to the ink, consumption required U.S. Pat.No. 4,799,068 on ink whereupon Low temperature May be damaged 1989 Miuraet al, electrostatic attraction by sparks due to air U.S. Pat. No.4,810,954 accelerates the ink breakdown Tone-jet towards the printRequired field medium. strength increases as the drop size decreasesHigh voltage drive transistors required Electrostatic field attractsdust Permanent An electromagnet Low power Complex IJ07, IJ10 magnetdirectly attracts a consumption fabrication electromagnetic permanentmagnet, Many ink types Permanent displacing ink and can be used magneticmaterial causing drop ejection. Fast operation such as Neodymium Rareearth magnets High efficiency Iron Boron (NdFeB) with a field strengthEasy extension required. around 1 Tesla can be from single nozzles Highlocal used. Examples are: to pagewidth print currents required SamariumCobalt heads Copper (SaCo) and magnetic metalization should materials inthe be used for long neodymium iron boron electromigration family(NdFeB, lifetime and low NdDyFeBNb, resistivity NdDyFeB, etc) Pigmentedinks are usually infeasible Operating temperature limited to the Curietemperature (around 540 K) Soft A solenoid induced a Low power ComplexIJ01, IJ05, IJ08, magnetic magnetic field in a soft consumptionfabrication IJ10, IJ12, IJ14, core electromagnetic magnetic core or yokeMany ink types Materials not IJ15, IJ17 fabricated from a can be usedusually present in a ferrous material such Fast operation CMOS fab suchas as electroplated iron High efficiency NiFe, CoNiFe, or alloys such asCoNiFe Easy extension CoFe are required [1], CoFe, or NiFe from singlenozzles High local alloys. Typically, the to pagewidth print currentsrequired soft magnetic material heads Copper is in two parts, whichmetalization should are normally held be used for long apart by aspring. electromigration When the solenoid is lifetime and low actuated,the two parts resistivity attract, displacing the Electroplating is ink.required High saturation flux density is required (2.0-2.1 T isachievable with CoNiFe [1]) Lorenz The Lorenz force Low power Force actsas a IJ06, IJ11, IJ13, force acting on a current consumption twistingmotion IJ16 carrying wire in a Many ink types Typically, only a magneticfield is can be used quarter of the utilized. Fast operation solenoidlength This allows the High efficiency provides force in a magneticfield to be Easy extension useful direction supplied externally to fromsingle nozzles High local the print head, for to pagewidth printcurrents required example with rare heads Copper earth permanentmetalization should magnets. be used for long Only the currentelectromigration carrying wire need be lifetime and low fabricated onthe print- resistivity head, simplifying Pigmented inks materials areusually requirements. infeasible Magnetostriction The actuator uses theMany ink types Force acts as a Fischenbeck, giant magnetostrictive canbe used twisting motion U.S. Pat. No. 4,032,929 effect of materials Fastoperation Unusual IJ25 such as Terfenol-D (an Easy extension materialssuch as alloy of terbium, from single nozzles Terfenol-D are dysprosiumand iron to pagewidth print required developed at the Naval heads Highlocal Ordnance Laboratory, High force is currents required henceTer-Fe-NOL). available Copper For best efficiency, the metalizationshould actuator should be pre- be used for long stressed to approx. 8MPa. electromigration lifetime and low resistivity Pre-stressing may berequired Surface Ink under positive Low power Requires Silverbrook, EPtension pressure is held in a consumption supplementary force 0771 658A2 and reduction nozzle by surface Simple to effect drop related patenttension. The surface construction separation applications tension of theink is No unusual Requires special reduced below the materials requiredin ink surfactants bubble threshold, fabrication Speed may be causingthe ink to High efficiency limited by surfactant egress from the Easyextension properties nozzle. from single nozzles to pagewidth printheads Viscosity The ink viscosity is Simple Requires Silverbrook, EPreduction locally reduced to construction supplementary force 0771 658A2 and select which drops are No unusual to effect drop related patentto be ejected. A materials required in separation applications viscosityreduction can fabrication Requires special be achieved Easy extensionink viscosity electrothermally with from single nozzles properties mostinks, but special to pagewidth print High speed is inks can beengineered heads difficult to achieve for a 100:1 viscosity Requiresreduction. oscillating ink pressure A high temperature difference(typically 80 degrees) is required Acoustic An acoustic wave is Canoperate Complex drive 1993 Hadimioglu generated and without a nozzlecircuitry et al, EUP 550,192 focussed upon the plate Complex 1993 Elrodet al, drop ejection region. fabrication EUP 572,220 Low efficiency Poorcontrol of drop position Poor control of drop volume Thermo- An actuatorwhich Low power Efficient aqueous IJ03, IJ09, IJ17, elastic bend reliesupon differential consumption operation requires a IJ18, IJ19, IJ20,actuator thermal expansion Many ink types thermal insulator on IJ21,IJ22, IJ23, upon Joule heating is can be used the hot side IJ24, IJ27,IJ28, used. Simple planar Corrosion IJ29, IJ30, IJ31, fabricationprevention can be IJ32, IJ33, IJ34, Small chip area difficult IJ35,IJ36, IJ37, required for each Pigmented inks IJ38, IJ39, IJ40, actuatormay be infeasible, IJ41 Fast operation as pigment particles Highefficiency may jam the bend CMOS actuator compatible voltages andcurrents Standard MEMS processes can be used Easy extension from singlenozzles to pagewidth print heads High CTE A material with a very Highforce can Requires special IJ09, IJ17, IJ18, thermo- high coefficient ofbe generated material (e.g. PTFE) IJ20, IJ21, IJ22, elastic thermalexpansion Three methods of Requires a PTFE IJ23, IJ24, IJ27, actuator(CTE) such as PTFE deposition are deposition process, IJ28, IJ29, IJ30,polytetrafluoroethylene under development: which is not yet IJ31, IJ42,IJ43, (PTFE) is used. As chemical vapor standard in ULSI IJ44 high CTEmaterials deposition (CVD), fabs are usually non- spin coating, and PTFEdeposition conductive, a heater evaporation cannot be followedfabricated from a PTFE is a with high conductive material is candidatefor low temperature (above incorporated. A 50 μm dielectric constant350° C.) processing long PTFE bend insulation in ULSI Pigmented inksactuator with Very low power may be infeasible, polysilicon heater andconsumption as pigment particles 15 mW power input Many ink types mayjam the bend can provide 180 μN can be used actuator force and 10 μmSimple planar deflection. Actuator fabrication motions include: Smallchip area Bend required for each Push actuator Buckle Fast operationRotate High efficiency CMOS compatible voltages and currents Easyextension from single nozzles to pagewidth print heads Conductive Apolymer with a high High force can Requires special IJ24 polymercoefficient of thermal be generated materials thermo- expansion (such asVery low power development (High elastic PTFE) is doped with consumptionCTE conductive actuator conducting substances Many ink types polymer) toincrease its can be used Requires a PTFE conductivity to about 3 Simpleplanar deposition process, orders of magnitude fabrication which is notyet below that of copper. Small chip area standard in ULSI Theconducting required for each fabs polymer expands actuator PTFEdeposition when resistively Fast operation cannot be followed heated.High efficiency with high Examples of CMOS temperature (above conductingdopants compatible voltages 350° C.) processing include: and currentsEvaporation and Carbon nanotubes Easy extension CVD deposition Metalfibers from single nozzles techniques cannot Conductive polymers topagewidth print be used such as doped heads Pigmented inks polythiophenemay be infeasible, Carbon granules as pigment particles may jam the bendactuator Shape A shape memory alloy High force is Fatigue limits IJ26memory such as TiNi (also available (stresses maximum number alloy knownas Nitinol - of hundreds of MPa) of cycles Nickel Titanium alloy Largestrain is Low strain (1%) developed at the Naval available (more than isrequired to extend Ordnance Laboratory) 3%) fatigue resistance isthermally switched High corrosion Cycle rate between its weak resistancelimited by heat martensitic state and Simple removal its high stiffnessconstruction Requires unusual austenic state. The Easy extensionmaterials (TiNi) shape of the actuator from single nozzles The latentheat of in its martensitic state to pagewidth print transformation mustis deformed relative to heads be provided the austenic shape. Lowvoltage High current The shape change operation operation causesejection of a Requires pre- drop. stressing to distort the martensiticstate Linear Linear magnetic Linear Magnetic Requires unusual IJ12Magnetic actuators include the actuators can be semiconductor ActuatorLinear Induction constructed with materials such as Actuator (LIA),Linear high thrust, long soft magnetic alloys Permanent Magnet travel,and high (e.g. CoNiFe) Synchronous Actuator efficiency using Somevarieties (LPMSA), Linear planar also require Reluctance semiconductorpermanent magnetic Synchronous Actuator fabrication materials such as(LRSA), Linear techniques Neodymium iron Switched Reluctance Longactuator boron (NdFeB) Actuator (LSRA), and travel is available Requiresthe Linear Stepper Medium force is complex multi- Actuator (LSA).available phase drive circuitry Low voltage High current operationoperation

BASIC OPERATION MODE Description Advantages Disadvantages ExamplesActuator This is the simplest Simple operation Drop repetition Thermalink jet directly mode of operation: the No external rate is usuallyPiezoelectric ink pushes ink actuator directly fields required limitedto around 10 kHz. jet supplies sufficient Satellite drops However, thisIJ01, IJ02, IJ03, kinetic energy to expel can be avoided if is notfundamental IJ04, IJ05, IJ06, the drop. The drop drop velocity is lessto the method, but is IJ07, IJ09, IJ11, must have a sufficient than 4m/s related to the refill IJ12, IJ14, IJ16, velocity to overcome Can beefficient, method normally IJ20, IJ22, IJ23, the surface tension.depending upon the used IJ24, IJ25, IJ26, actuator used All of the dropIJ27, IJ28, IJ29, kinetic energy must IJ30, IJ31, IJ32, be provided bythe IJ33, IJ34, IJ35, actuator IJ36, IJ37, IJ38, Satellite drops IJ39,IJ40, IJ41, usually form if drop IJ42, IJ43, IJ44 velocity is greaterthan 4.5 m/s Proximity The drops to be Very simple print Requires closeSilverbrook, EP printed are selected by head fabrication can proximitybetween 0771 658 A2 and some manner (e.g. be used the print head andrelated patent thermally induced The drop the print media orapplications surface tension selection means transfer roller reductionof does not need to May require two pressurized ink). provide the energyprint heads printing Selected drops are required to separate alternaterows of the separated from the ink the drop from the image in the nozzleby nozzle Monolithic color contact with the print print heads are mediumor a transfer difficult roller. Electrostatic The drops to be Verysimple print Requires very Silverbrook, EP pull printed are selected byhead fabrication can high electrostatic 0771 658 A2 and on ink somemanner (e.g. be used field related patent thermally induced The dropElectrostatic field applications surface tension selection means forsmall nozzle Tone-Jet reduction of does not need to sizes is above airpressurized ink). provide the energy breakdown Selected drops arerequired to separate Electrostatic field separated from the ink the dropfrom the may attract dust in the nozzle by a nozzle strong electricfield. Magnetic The drops to be Very simple print Requires Silverbrook,EP pull on ink printed are selected by head fabrication can magnetic ink0771 658 A2 and some manner (e.g. be used Ink colors other relatedpatent thermally induced The drop than black are applications surfacetension selection means difficult reduction of does not need to Requiresvery pressurized ink). provide the energy high magnetic fields Selecteddrops are required to separate separated from the ink the drop from thein the nozzle by a nozzle strong magnetic field acting on the magneticink. Shutter The actuator moves a High speed (>50 kHz) Moving parts areIJ13, IJ17, IJ21 shutter to block ink operation can required flow to thenozzle. The be achieved due to Requires ink ink pressure is pulsedreduced refill time pressure modulator at a multiple of the Drop timingcan Friction and wear drop ejection be very accurate must be consideredfrequency. The actuator Stiction is energy can be very possible lowShuttered The actuator moves a Actuators with Moving parts are IJ08,IJ15, IJ18, grill shutter to block ink small travel can be required IJ19flow through a grill to used Requires ink the nozzle. The shutterActuators with pressure modulator movement need only small force can beFriction and wear be equal to the width used must be considered of thegrill holes. High speed (>50 kHz) Stiction is operation can possible beachieved Pulsed A pulsed magnetic Extremely low Requires an IJ10magnetic field attracts an ‘ink energy operation is external pulsed pullon ink pusher’ at the drop possible magnetic field pusher ejectionfrequency. An No heat Requires special actuator controls a dissipationmaterials for both catch, which prevents problems the actuator and thethe ink pusher from ink pusher moving when a drop is Complex not to beejected. construction

AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) Description AdvantagesDisadvantages Examples None The actuator directly Simplicity of Dropejection Most ink jets, fires the ink drop, and construction energy mustbe including there is no external Simplicity of supplied bypiezoelectric and field or other operation individual nozzle thermalbubble. mechanism required. Small physical actuator IJ01, IJ02, IJ03,size IJ04, IJ05, IJ07, IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24,IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36,IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating The inkpressure Oscillating ink Requires external Silverbrook, EP ink pressureoscillates, providing pressure can provide ink pressure 0771 658 A2 and(including much of the drop a refill pulse, oscillator related patentacoustic ejection energy. The allowing higher Ink pressure applicationsstimulation) actuator selects which operating speed phase and amplitudeIJ08, IJ13, IJ15, drops are to be fired The actuators must be carefullyIJ17, IJ18, IJ19, by selectively may operate with controlled IJ21blocking or enabling much lower energy Acoustic nozzles. The inkAcoustic lenses reflections in the ink pressure oscillation can be usedto focus chamber must be may be achieved by the sound on the designedfor vibrating the print nozzles head, or preferably by an actuator inthe ink supply. Media The print head is Low power Precision Silverbrook,EP proximity placed in close High accuracy assembly required 0771 658 A2and proximity to the print Simple print head Paper fibers may relatedpatent medium. Selected construction cause problems applications dropsprotrude from Cannot print on the print head further rough substratesthan unselected drops, and contact the print medium. The drop soaks intothe medium fast enough to cause drop separation. Transfer Drops areprinted to a High accuracy Bulky Silverbrook, EP roller transfer rollerinstead Wide range of Expensive 0771 658 A2 and of straight to the printprint substrates can Complex related patent medium. A transfer be usedconstruction applications roller can also be used Ink can be driedTektronix hot for proximity drop on the transfer roller meltpiezoelectric separation. ink jet Any of the IJ series Electrostatic Anelectric field is Low power Field strength Silverbrook, EP used toaccelerate Simple print head required for 0771 658 A2 and selected dropstowards construction separation of small related patent the printmedium. drops is near or applications above air Tone-Jet breakdownDirect A magnetic field is Low power Requires Silverbrook, EP magneticused to accelerate Simple print head magnetic ink 0771 658 A2 and fieldselected drops of construction Requires strong related patent magneticink towards magnetic field applications the print medium. Cross Theprint head is Does not require Requires external IJ06, IJ16 magneticplaced in a constant magnetic materials magnet field magnetic field. Theto be integrated in Current densities Lorenz force in a the print headmay be high, current carrying wire manufacturing resulting in is used tomove the process electromigration actuator. problems Pulsed A pulsedmagnetic Very low power Complex print IJ10 magnetic field is used tooperation is possible head construction field cyclically attract a Smallprint head Magnetic paddle, which pushes size materials required in onthe ink. A small print head actuator moves a catch, which selectivelyprevents the paddle from moving.

ACTUATOR AMPLIFICATION OR MODIFICATION METHOD Description AdvantagesDisadvantages Examples None No actuator Operational Many actuatorThermal Bubble mechanical simplicity mechanisms have Ink jetamplification is used. insufficient travel, IJ01, IJ02, IJ06, Theactuator directly or insufficient force, IJ07, IJ16, IJ25, drives thedrop to efficiently drive IJ26 ejection process. the drop ejectionprocess Differential An actuator material Provides greater High stressesare Piezoelectric expansion expands more on one travel in a reducedinvolved IJ03, IJ09, IJ17, bend side than on the other. print head areaCare must be IJ18, IJ19, IJ20, actuator The expansion may be taken thatthe IJ21, IJ22, IJ23, thermal, piezoelectric, materials do not IJ24,IJ27, IJ29, magnetostrictive, or delaminate IJ30, IJ31, IJ32, othermechanism. The Residual bend IJ33, IJ34, IJ35, bend actuator convertsresulting from high IJ36, IJ37, IJ38, a high force low traveltemperature or high IJ39, IJ42, IJ43, actuator mechanism to stressduring IJ44 high travel, lower formation force mechanism. Transient Atrilayer bend Very good High stresses are IJ40, IJ41 bend actuator wherethe two temperature stability involved actuator outside layers are Highspeed, as a Care must be identical. This cancels new drop can be takenthat the bend due to ambient fired before heat materials do nottemperature and dissipates delaminate residual stress. The Cancelsresidual actuator only responds stress of formation to transient heatingof one side or the other. Reverse The actuator loads a Better couplingFabrication IJ05, IJ11 spring spring. When the to the ink complexityactuator is turned off, High stress in the the spring releases. springThis can reverse the force/distance curve of the actuator to make itcompatible with the force/time requirements of the drop ejection.Actuator A series of thin Increased travel Increased Some stackactuators are stacked. Reduced drive fabrication piezoelectric ink jetsThis can be voltage complexity IJ04 appropriate where Increasedactuators require high possibility of short electric field strength,circuits due to such as electrostatic pinholes and piezoelectricactuators. Multiple Multiple smaller Increases the Actuator forces IJ12,IJ13, IJ18, actuators actuators are used force available from may notadd IJ20, IJ22, IJ28, simultaneously to an actuator linearly, reducingIJ42, IJ43 move the ink. Each Multiple efficiency actuator need provideactuators can be only a portion of the positioned to control forcerequired. ink flow accurately Linear A linear spring is used Matches lowRequires print IJ15 Spring to transform a motion travel actuator withhead area for the with small travel and higher travel spring high forceinto a requirements longer travel, lower Non-contact force motion.method of motion transformation Coiled A bend actuator is Increasestravel Generally IJ17, IJ21, IJ34, actuator coiled to provide Reduceschip restricted to planar IJ35 greater travel in a area implementationsreduced chip area. Planar due to extreme implementations are fabricationdifficulty relatively easy to in other orientations. fabricate. FlexureA bend actuator has a Simple means of Care must be IJ10, IJ19, IJ33 bendsmall region near the increasing travel of taken not to exceed actuatorfixture point, which a bend actuator the elastic limit in flexes muchmore the flexure area readily than the Stress remainder of thedistribution is very actuator. The actuator uneven flexing iseffectively Difficult to converted from an accurately model even coilingto an with finite element angular bend, resulting analysis in greatertravel of the actuator tip. Catch The actuator controls a Very lowComplex IJ10 small catch. The catch actuator energy construction eitherenables or Very small Requires external disables movement of actuatorsize force an ink pusher that is Unsuitable for controlled in a bulkpigmented inks manner. Gears Gears can be used to Low force, low Movingparts are IJ13 increase travel at the travel actuators can requiredexpense of duration. be used Several actuator Circular gears, rack Canbe fabricated cycles are required and pinion, ratchets, using standardMore complex and other gearing surface MEMS drive electronics methodscan be used. processes Complex construction Friction, friction, and wearare possible Buckle plate A buckle plate can be Very fast Must staywithin S. Hirata et al, used to change a slow movement elastic limits ofthe “An Ink-jet Head actuator into a fast achievable materials for longUsing Diaphragm motion. It can also device life Microactuator”, converta high force, High stresses Proc. IEEE MEMS, low travel actuatorinvolved February 1996, pp 418-423. into a high travel, Generally highIJ18, IJ27 medium force motion. power requirement Tapered A taperedmagnetic Linearizes the Complex IJ14 magnetic pole can increase magneticconstruction pole travel at the expense force/distance curve of force.Lever A lever and fulcrum is Matches low High stress IJ32, IJ36, IJ37used to transform a travel actuator with around the fulcrum motion withsmall higher travel travel and high force requirements into a motionwith Fulcrum area has longer travel and no linear movement, lower force.The lever and can be used for can also reverse the a fluid sealdirection of travel. Rotary The actuator is High mechanical Complex IJ28impeller connected to a rotary advantage construction impeller. A smallThe ratio of force Unsuitable for angular deflection of to travel of thepigmented inks the actuator results in actuator can be a rotation of thematched to the impeller vanes, which nozzle requirements push the inkagainst by varying the stationary vanes and number of impeller out ofthe nozzle. vanes Acoustic A refractive or No moving parts Large area1993 Hadimioglu lens diffractive (e.g. zone required et al, EUP 550,192plate) acoustic lens is Only relevant for 1993 Elrod et al, used toconcentrate acoustic ink jets EUP 572,220 sound waves. Sharp A sharppoint is used Simple Difficult to Tone-jet conductive to concentrate anconstruction fabricate using point electrostatic field. standard VLSIprocesses for a surface ejecting ink- jet Only relevant forelectrostatic ink jets

ACTUATOR MOTION Description Advantages Disadvantages Examples Volume Thevolume of the Simple High energy is Hewlett-Packard expansion actuatorchanges, construction in the typically required to Thermal Ink jetpushing the ink in all case of thermal ink achieve volume CanonBubblejet directions. jet expansion. This leads to thermal stress,cavitation, and kogation in thermal ink jet implementations Linear, Theactuator moves in Efficient High fabrication IJ01, IJ02, IJ04, normal toa direction normal to coupling to ink complexity may be IJ07, IJ11, IJ14chip surface the print head surface. drops ejected required to achieveThe nozzle is typically normal to the perpendicular in the line ofsurface motion movement. Parallel to The actuator moves Suitable forFabrication IJ12, IJ13, IJ15, chip surface parallel to the print planarfabrication complexity IJ33,, IJ34, IJ35, head surface. Drop FrictionIJ36 ejection may still be Stiction normal to the surface. Membrane Anactuator with a The effective Fabrication 1982 Howkins push high forcebut small area of the actuator complexity U.S. Pat. No. 4,459,601 areais used to push a becomes the Actuator size stiff membrane that ismembrane area Difficulty of in contact with the ink. integration in aVLSI process Rotary The actuator causes Rotary levers Device IJ05, IJ08,IJ13, the rotation of some may be used to complexity IJ28 element, sucha grill or increase travel May have impeller Small chip area friction ata pivot requirements point Bend The actuator bends A very small Requiresthe 1970 Kyser et al when energized. This change in actuator to be madeU.S. Pat. No. 3,946,398 may be due to dimensions can be from at leasttwo 1973 Stemme differential thermal converted to a large distinctlayers, or to U.S. Pat. No. 3,747,120 expansion, motion. have a thermalIJ03, IJ09, IJ10, piezoelectric difference across the IJ19, IJ23, IJ24,expansion, actuator IJ25, IJ29, IJ30, magnetostriction, or IJ31, IJ33,IJ34, other form of relative IJ35 dimensional change. Swivel Theactuator swivels Allows operation Inefficient IJ06 around a centralpivot. where the net linear coupling to the ink This motion is suitableforce on the paddle motion where there are is zero opposite forces Smallchip area applied to opposite requirements sides of the paddle, e.g.Lorenz force. Straighten The actuator is Can be used with Requirescareful IJ26, IJ32 normally bent, and shape memory balance of stressesstraightens when alloys where the to ensure that the energized. austenicphase is quiescent bend is planar accurate Double The actuator bends inOne actuator can Difficult to make IJ36, IJ37, IJ38 bend one directionwhen be used to power the drops ejected by one element is two nozzles.both bend directions energized, and bends Reduced chip identical. theother way when size. A small another element is Not sensitive toefficiency loss energized. ambient temperature compared to equivalentsingle bend actuators. Shear Energizing the Can increase the Not readily1985 Fishbeck actuator causes a shear effective travel of applicable toother U.S. Pat. No. 4,584,590 motion in the actuator piezoelectricactuator material. actuators mechanisms Radial constriction The actuatorsqueezes Relatively easy High force 1970 Zoltan U.S. Pat. No. an inkreservoir, to fabricate single required 3,683,212 forcing ink from anozzles from glass Inefficient constricted nozzle. tubing as Difficultto macroscopic integrate with VLSI structures processes Coil/uncoil Acoiled actuator Easy to fabricate Difficult to IJ17, IJ21, IJ34, uncoilsor coils more as a planar VLSI fabricate for non- IJ35 tightly. Themotion of process planar devices the free end of the Small area Poorout-of-plane actuator ejects the ink. required, therefore stiffness lowcost Bow The actuator bows (or Can increase the Maximum travel IJ16,IJ18, IJ27 buckles) in the middle speed of travel is constrained whenenergized. Mechanically High force rigid required Push-Pull Twoactuators control The structure is Not readily IJ18 a shutter. Oneactuator pinned at both ends, suitable for ink jets pulls the shutter,and so has a high out-of- which directly push the other pushes it. planerigidity the ink Curl A set of actuators curl Good fluid flow DesignIJ20, IJ42 inwards inwards to reduce the to the region behind complexityvolume of ink that the actuator they enclose. increases efficiency CurlA set of actuators curl Relatively simple Relatively large IJ43 outwardsoutwards, pressurizing construction chip area ink in a chambersurrounding the actuators, and expelling ink from a nozzle in thechamber. Iris Multiple vanes enclose High efficiency High fabricationIJ22 a volume of ink. These Small chip area complexity simultaneouslyrotate, Not suitable for reducing the volume pigmented inks between thevanes. Acoustic The actuator vibrates The actuator can Large area 1993Hadimioglu vibration at a high frequency. be physically distant requiredfor et al, EUP 550,192 from the ink efficient operation 1993 Elrod etal, at useful frequencies EUP 572,220 Acoustic coupling and crosstalkComplex drive circuitry Poor control of drop volume and position None Invarious ink jet No moving parts Various other Silverbrook, EP designsthe actuator tradeoffs are 0771 658 A2 and does not move. required torelated patent eliminate moving applications parts Tone-jet

NOZZLE REFILL METHOD Description Advantages Disadvantages ExamplesSurface This is the normal way Fabrication Low speed Thermal ink jettension that ink jets are simplicity Surface tension Piezoelectric inkrefilled. After the Operational force relatively jet actuator isenergized, simplicity small compared to IJ01-IJ07, IJ10-IJ14, ittypically returns actuator force IJ16, IJ20, rapidly to its normal Longrefill time IJ22-IJ45 position. This rapid usually dominates returnsucks in air the total repetition through the nozzle rate opening. Theink surface tension at the nozzle then exerts a small force restoringthe meniscus to a minimum area. This force refills the nozzle. ShutteredInk to the nozzle High speed Requires IJ08, IJ13, IJ15, oscillatingchamber is provided at Low actuator common ink IJ17, IJ18, IJ19, inkpressure a pressure that energy, as the pressure oscillator IJ21oscillates at twice the actuator need only May not be drop ejection openor close the suitable for frequency. When a shutter, instead ofpigmented inks drop is to be ejected, ejecting the ink drop the shutteris opened for 3 half cycles: drop ejection, actuator return, and refill.The shutter is then closed to prevent the nozzle chamber emptying duringthe next negative pressure cycle. Refill After the main High speed, asRequires two IJ09 actuator actuator has ejected a the nozzle isindependent drop a second (refill) actively refilled actuators pernozzle actuator is energized. The refill actuator pushes ink into thenozzle chamber. The refill actuator returns slowly, to prevent itsreturn from emptying the chamber again. Positive ink The ink is held aslight High refill rate, Surface spill Silverbrook, EP pressure positivepressure. therefore a high must be prevented 0771 658 A2 and After theink drop is drop repetition rate Highly related patent ejected, thenozzle is possible hydrophobic print applications chamber fills quicklyhead surfaces are Alternative for:, as surface tension and requiredIJ01-IJ07, IJ10-IJ14, ink pressure both IJ16, IJ20, IJ22-IJ45 operate torefill the nozzle.

METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Description AdvantagesDisadvantages Examples Long inlet The ink inlet channel Designsimplicity Restricts refill Thermal ink jet channel to the nozzlechamber Operational rate Piezoelectric ink is made long and simplicityMay result in a jet relatively narrow, Reduces relatively large chipIJ42, IJ43 relying on viscous crosstalk area drag to reduce inlet Onlypartially back-flow. effective Positive ink The ink is under a Dropselection Requires a Silverbrook, EP pressure positive pressure, so andseparation method (such as a 0771 658 A2 and that in the quiescentforces can be nozzle rim or related patent state some of the ink reducedeffective applications drop already protrudes Fast refill timehydrophobizing, or Possible from the nozzle. both) to prevent operationof the This reduces the flooding of the following: IJ01-IJ07, pressurein the nozzle ejection surface of IJ09-IJ12, chamber which is the printhead. IJ14, IJ16, IJ20, required to eject a IJ22,, IJ23-IJ34, certainvolume of ink. IJ36-IJ41, IJ44 The reduction in chamber pressure resultsin a reduction in ink pushed out through the inlet. Baffle One or morebaffles The refill rate is Design HP Thermal Ink are placed in the inletnot as restricted as complexity Jet ink flow. When the the long inletMay increase Tektronix actuator is energized, method. fabricationpiezoelectric ink jet the rapid ink Reduces complexity (e.g. movementcreates crosstalk Tektronix hot melt eddies which restrict Piezoelectricprint the flow through the heads). inlet. The slower refill process isunrestricted, and does not result in eddies. Flexible flap In thismethod recently Significantly Not applicable to Canon restrictsdisclosed by Canon, reduces back-flow most ink jet inlet the expandingactuator for edge-shooter configurations (bubble) pushes on a thermalink jet Increased flexible flap that devices fabrication restricts theinlet. complexity Inelastic deformation of polymer flap results in creepover extended use Inlet filter A filter is located Additional Restrictsrefill IJ04, IJ12, IJ24, between the ink inlet advantage of ink rateIJ27, IJ29, IJ30 and the nozzle filtration May result in chamber. Thefilter Ink filter may be complex has a multitude of fabricated with noconstruction small holes or slots, additional process restricting inkflow. steps The filter also removes particles which may block thenozzle. Small inlet The ink inlet channel Design simplicity Restrictsrefill IJ02, IJ37, IJ44 compared to the nozzle chamber rate to nozzlehas a substantially May result in a smaller cross section relativelylarge chip than that of the nozzle, area resulting in easier ink Onlypartially egress out of the effective nozzle than out of the inlet.Inlet shutter A secondary actuator Increases speed Requires separateIJ09 controls the position of of the ink-jet print refill actuator and ashutter, closing off head operation drive circuit the ink inlet when themain actuator is energized. The inlet is The method avoids the Back-flowRequires careful IJ01, IJ03, 1J05, located problem of inlet back-problem is design to minimize IJ06, IJ07, IJ10, behind the flow byarranging the eliminated the negative IJ11, IJ14, IJ16, ink-pushingink-pushing surface of pressure behind the IJ22, IJ23, IJ25, surface theactuator between paddle IJ28, IJ31, IJ32, the inlet and the IJ33, IJ34,IJ35, nozzle. IJ36, IJ39, IJ40, IJ41 Part of the The actuator and aSignificant Small increase in IJ07, IJ20, IJ26, actuator wall of the inkreductions in back- fabrication IJ38 moves to chamber are arranged flowcan be complexity shut off the so that the motion of achieved inlet theactuator closes off Compact designs the inlet. possible Nozzle In someconfigurations Ink back-flow None related to Silverbrook, EP actuator ofink jet, there is no problem is ink back-flow on 0771 658 A2 and doesnot expansion or eliminated actuation related patent result in inkmovement of an applications back-flow actuator which may Valve-jet causeink back-flow Tone-jet through the inlet.

NOZZLE CLEARING METHOD Description Advantages Disadvantages ExamplesNormal All of the nozzles are No added May not be Most ink jet nozzlefiring fired periodically, complexity on the sufficient to systemsbefore the ink has a print head displace dried ink IJ01, IJ02, IJ03,chance to dry. When IJ04, IJ05, IJ06, not in use the nozzles IJ07, IJ09,IJ10, are sealed (capped) IJ11, IJ12, IJ14, against air. IJ16, IJ20,IJ22, The nozzle firing is IJ23, IJ24, IJ25, usually performed IJ26,IJ27, IJ28, during a special IJ29, IJ30, IJ31, clearing cycle, afterIJ32, IJ33, IJ34, first moving the print IJ36, IJ37, IJ38, head to acleaning IJ39, IJ40,, IJ41, station. IJ42, IJ43, IJ44,, IJ45 Extra Insystems which heat Can be highly Requires higher Silverbrook, EP powerto the ink, but do not boil effective if the drive voltage for 0771 658A2 and ink heater it under normal heater is adjacent to clearing relatedpatent situations, nozzle the nozzle May require applications clearingcan be larger drive achieved by over- transistors powering the heaterand boiling ink at the nozzle. Rapid The actuator is fired in Does notrequire Effectiveness May be used succession rapid succession. In extradrive circuits depends with: IJ01, IJ02, of actuator someconfigurations, on the print head substantially upon IJ03, IJ04, IJ05,pulses this may cause heat Can be readily the configuration of IJ06,IJ07, IJ09, build-up at the nozzle controlled and the ink jet nozzleIJ10, IJ11, IJ14, which boils the ink, initiated by digital IJ16, IJ20,IJ22, clearing the nozzle. In logic IJ23, IJ24, IJ25, other situations,it may IJ27, IJ28, IJ29, cause sufficient IJ30, IJ31, IJ32, vibrationsto dislodge IJ33, IJ34, IJ36, clogged nozzles. IJ37, IJ38, IJ39, IJ40,IJ41, IJ42, IJ43, IJ44, IJ45 Extra Where an actuator is A simple Notsuitable May be used power to not normally driven to solution wherewhere there is a with: IJ03, IJ09, ink pushing the limit of its motion,applicable hard limit to IJ16, IJ20, IJ23, actuator nozzle clearing maybe actuator movement IJ24, IJ25, IJ27, assisted by providing IJ29, IJ30,IJ31, an enhanced drive IJ32, IJ39, IJ40, signal to the actuator. IJ41,IJ42, IJ43, IJ44, IJ45 Acoustic An ultrasonic wave is A high nozzle HighIJ08, IJ13, IJ15, resonance applied to the ink clearing capabilityimplementation cost IJ17, IJ18, IJ19, chamber. This wave is can beachieved if system does not IJ21 of an appropriate May be alreadyinclude an amplitude and implemented at very acoustic actuator frequencyto cause low cost in systems sufficient force at the which alreadynozzle to clear include acoustic blockages. This is actuators easiest toachieve if the ultrasonic wave is at a resonant frequency of the inkcavity. Nozzle A microfabricated Can clear Accurate Silverbrook, EPclearing plate is pushed against severely clogged mechanical 0771 658 A2and plate the nozzles. The plate nozzles alignment is related patent hasa post for every required applications nozzle. A post moves Moving partsare through each nozzle, required displacing dried ink. There is risk ofdamage to the nozzles Accurate fabrication is required Ink The pressureof the ink May be effective Requires May be used pressure is temporarilywhere other pressure pump or with all IJ series ink pulse increased sothat ink methods cannot be other pressure jets streams from all of theused actuator nozzles. This may be Expensive used in conjunctionWasteful of ink with actuator energizing. Print head A flexible ‘blade’is Effective for Difficult to use if Many ink jet wiper wiped across theprint planar print head print head surface is systems head surface. Thesurfaces non-planar or very blade is usually Low cost fragile fabricatedfrom a Requires flexible polymer, e.g. mechanical parts rubber orsynthetic Blade can wear elastomer. out in high volume print systemsSeparate A separate heater is Can be effective Fabrication Can be usedwith ink boiling provided at the nozzle where other nozzle complexitymany IJ series ink heater although the normal clearing methods jets drope-ection cannot be used mechanism does not Can be require it. Theheaters implemented at no do not require additional cost in individualdrive some ink jet circuits, as many configurations nozzles can becleared simultaneously, and no imaging is required.

NOZZLE PLATE CONSTRUCTION Description Advantages Disadvantages ExamplesElectroformed A nozzle plate is Fabrication High Hewlett Packard nickelseparately fabricated simplicity temperatures and Thermal Ink jet fromelectroformed pressures are nickel, and bonded to required to bond theprint head chip. nozzle plate Minimum thickness constraints Differentialthermal expansion Laser Individual nozzle No masks Each hole must CanonBubblejet ablated or holes are ablated by an required be individually1988 Sercel et drilled intense UV laser in a Can be quite fast formedal., SPIE, Vol. 998 polymer nozzle plate, which is Some control SpecialExcimer Beam typically a polymer over nozzle profile equipment requiredApplications, pp. such as polyimide or is possible Slow where there76-83 polysulphone Equipment are many thousands 1993 Watanabe requiredis relatively of nozzles per print et al., U.S. Pat. No. low cost head5,208,604 May produce thin burrs at exit holes Silicon A separate nozzleHigh accuracy is Two part K. Bean, IEEE micromachined plate isattainable construction Transactions on micromachined from High costElectron Devices, single crystal silicon, Requires Vol. ED-25, No. 10,and bonded to the precision alignment 1978, pp 1185-1195 print headwafer. Nozzles may be Xerox 1990 clogged by adhesive Hawkins et al.,U.S. Pat. No. 4,899,181 Glass Fine glass capillaries No expensive Verysmall 1970 Zoltan U.S. Pat. No. capillaries are drawn from glassequipment required nozzle sizes are 3,683,212 tubing. This method Simpleto make difficult to form has been used for single nozzles Not suitedfor making individual mass production nozzles, but is difficult to usefor bulk manufacturing of print heads with thousands of nozzles.Monolithic, The nozzle plate is High accuracy Requires Silverbrook, EPsurface deposited as a layer (<1 μm) sacrificial layer 0771 658 A2 andmicromachined using standard VLSI Monolithic under the nozzle relatedpatent using VLSI deposition techniques. Low cost plate to form theapplications lithographic Nozzles are etched in Existing nozzle chamberIJ01, IJ02, IJ04, processes the nozzle plate using processes can beSurface may be IJ11, IJ12, IJ17, VLSI lithography and used fragile tothe touch IJ18, IJ20, IJ22, etching. IJ24, IJ27, IJ28, IJ29, IJ30, IJ31,IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44Monolithic, The nozzle plate is a High accuracy Requires long IJ03,IJ05, IJ06, etched buried etch stop in the (<1 μm) etch times IJ07,IJ08, IJ09, through wafer. Nozzle Monolithic Requires a IJ10, IJ13,IJ14, substrate chambers are etched in Low cost support wafer IJ15,IJ16, IJ19, the front of the wafer, No differential IJ21, IJ23, IJ25,and the wafer is expansion IJ26 thinned from the back side. Nozzles arethen etched in the etch stop layer. No nozzle Various methods have Nonozzles to Difficult to Ricoh 1995 plate been tried to eliminate becomeclogged control drop Sekiya et al U.S. Pat. No. the nozzles entirely, toposition accurately 5,412,413 prevent nozzle Crosstalk 1993 Hadimiogluclogging. These problems et al EUP 550,192 include thermal bubble 1993Elrod et al mechanisms and EUP 572,220 acoustic lens mechanisms TroughEach drop ejector has Reduced Drop firing IJ35 a trough throughmanufacturing direction is sensitive which a paddle moves. complexity towicking. There is no nozzle Monolithic plate. Nozzle slit Theelimination of No nozzles to Difficult to 1989 Saito et al instead ofnozzle holes and become clogged control drop U.S. Pat. No. 4,799,068individual replacement by a slit position accurately nozzlesencompassing many Crosstalk actuator positions problems reduces nozzleclogging, but increases crosstalk due to ink surface waves

DROP EJECTION DIRECTION Description Advantages Disadvantages ExamplesEdge Ink flow is along the Simple Nozzles limited Canon Bubblejet (‘edgesurface of the chip, construction to edge 1979 Endo et al GB shooter’)and ink drops are No silicon High resolution patent 2,007,162 ejectedfrom the chip etching required is difficult Xerox heater-in- edge. Goodheat Fast color pit 1990 Hawkins et sinking via substrate printingrequires al U.S. Pat. No. 4,899,181 Mechanically one print head perTone-jet strong color Ease of chip handing Surface Ink flow is along theNo bulk silicon Maximum ink Hewlett-Packard (‘roof surface of the chip,etching required flow is severely TIJ 1982 Vaught et shooter’) and inkdrops are Silicon can make restricted al U.S. Pat. No. 4,490,728 ejectedfrom the chip an effective heat IJ02, IJ11, IJ12, surface, normal to thesink IJ20, IJ22 plane of the chip. Mechanical strength Through Ink flowis through the High ink flow Requires bulk Silverbrook, EP chip, chip,and ink drops are Suitable for silicon etching 0771 658 A2 and forwardejected from the front pagewidth print related patent (‘up surface ofthe chip. heads applications shooter’) High nozzle IJ04, IJ17, IJ18,packing density IJ24, IJ27-IJ45 therefore low manufacturing cost ThroughInk flow is through the High ink flow Requires wafer IJ01, IJ03, IJ05,chip, chip, and ink drops are Suitable for thinning IJ06, IJ07, IJ08,reverse ejected from the rear pagewidth print Requires special IJ09,IJ10, IJ13, (‘down surface of the chip. heads handling during IJ14,IJ15, IJ16, shooter’) High nozzle manufacture IJ19, IJ21, IJ23, packingdensity IJ25, IJ26 therefore low manufacturing cost Through Ink flow isthrough the Suitable for Pagewidth print Epson Stylus actuator actuator,which is not piezoelectric print heads require Tektronix hot fabricatedas part of heads several thousand melt piezoelectric the same substrateas connections to drive ink jets the drive transistors. circuits Cannotbe manufactured in standard CMOS fabs Complex assembly required

INK TYPE Description Advantages Disadvantages Examples Aqueous, Waterbased ink which Environmentally Slow drying Most existing ink dyetypically contains: friendly Corrosive jets water, dye, surfactant, Noodor Bleeds on paper All IJ series ink humectant, and May jets biocide.strikethrough Silverbrook, EP Modern ink dyes have Cockles paper 0771658 A2 and high water-fastness, related patent light fastnessapplications Aqueous, Water based ink which Environmentally Slow dryingIJ02, IJ04, IJ21, pigment typically contains: friendly Corrosive IJ26,IJ27, IJ30 water, pigment, No odor Pigment may Silverbrook, EPsurfactant, humectant, Reduced bleed clog nozzles 0771 658 A2 and andbiocide. Reduced wicking Pigment may related patent Pigments have anReduced clog actuator applications advantage in reduced strikethroughmechanisms Piezoelectric ink- bleed, wicking and Cockles paper jetsstrikethrough. Thermal ink jets (with significant restrictions) MethylMEK is a highly Very fast drying Odorous All IJ series ink Ethylvolatile solvent used Prints on various Flammable jets Ketone forindustrial printing substrates such as (MEK) on difficult surfacesmetals and plastics such as aluminum cans. Alcohol Alcohol based inksFast drying Slight odor All IJ series ink (ethanol, 2- can be used wherethe Operates at sub- Flammable jets butanol, printer must operate atfreezing and others) temperatures below temperatures the freezing pointof Reduced paper water. An example of cockle this is in-camera Low costconsumer photographic printing. Phase The ink is solid at No dryingtime- High viscosity Tektronix hot change room temperature, and inkinstantly freezes Printed ink melt piezoelectric (hot melt) is melted inthe print on the print medium typically has a ink jets head beforejetting. Almost any print ‘waxy’ feel 1989 Nowak Hot melt inks aremedium can be used Printed pages U.S. Pat. No. 4,820,346 usually waxbased, No paper cockle may ‘block’ All IJ series ink with a meltingpoint occurs Ink temperature jets around 80° C. After No wicking may beabove the jetting the ink freezes occurs curie point of almost instantlyupon No bleed occurs permanent magnets contacting the print Nostrikethrough Ink heaters medium or a transfer occurs consume powerroller. Long warm-up time Oil Oil based inks are High solubility Highviscosity: All IJ series ink extensively used in medium for some this isa significant jets offset printing. They dyes limitation for use in haveadvantages in Does not cockle ink jets, which improved paper usuallyrequire a characteristics on Does not wick low viscosity. Some paper(especially no through paper short chain and wicking or cockle).multi-branched oils Oil soluble dies and have a sufficiently pigmentsare required. low viscosity. Slow drying Microemulsion A microemulsionis a Stops ink bleed Viscosity higher All IJ series ink stable, selfforming High dye than water jets emulsion of oil, water, solubility Costis slightly and surfactant. The Water, oil, and higher than watercharacteristic drop size amphiphilic soluble based ink is less than 100nm, dies can be used High surfactant and is determined by Can stabilizeconcentration the preferred curvature pigment required (around of thesurfactant. suspensions 5%)

1. A micro-electromechanical valve comprising: a channel defined by asubstrate and by circuitry on the substrate so as to terminate at anaperture; a closure member arranged to be displaceable between first andsecond positions at which the aperture is respectively covered anduncovered and fluid is respectively inhibited and permitted from flowingthrough the channel; and an elongate actuator for displacing the closuremember between the first and second positions, the actuator anchored atone end to the substrate and connected to the closure member at theother end, wherein a portion of the actuator is in electrical contactwith the circuitry, the portion being configured to transform betweenstraightened and arcuate shapes when respectively heated and cooled byrespective receipt and withdrawal of electrical current from thecircuitry, the actuator displacing the closure member between the firstand second positions in response to the transformation of the portion.2. A valve as claimed in claim 1, wherein the actuator incorporatesresiliently flexible material having a coefficient of thermal expansionwhich is such that the material expands to perform work when heated,said portion being positioned in the material and defining a heatingcircuit.
 3. A valve as claimed in claim 2, wherein the heating circuitincorporates a heater and a return trace, the heater being positionedproximate an inside edge of the material and the return trace beingpositioned outwardly of the heater, so that an inside region of thematerial is heated to a relatively greater extent with the result thatthe inside region expands to a greater extent than a remainder of thematerial.
 4. A valve as claimed in claim 3, wherein the heater isdefined by a serpentine length of metal.
 5. A valve as claimed in claim3, wherein the material is polytetrafluoroethylene and the heatingcircuit is formed of copper.
 6. A valve as claimed in claim 1, whereinthe actuator defines a coil that partially uncoils when said portiontransforms from the arcuate shape to the straightened shape.